1. Field of the Invention
The present invention relates to a zoom lens barrel and an optical instrument using the barrel, such as a still camera, a digital still camera, and a video camera.
2. Description of the Related Art
In an imaging device such as a digital camera, a so-called collapsible lens barrel has been used in that during imaging, a lens barrel is extended from an imaging device body while during carrying (non-imaging), the lens barrel is accommodated into the imaging device body.
Such a lens barrel is disclosed in Japanese Patent Laid-Open No. 2001-324663, in which a movable cam ring is provided with a cam groove for moving a lens; a fixed cylinder is provided with a collapsing cam groove; and the movable cam ring is rotated along the collapsing cam groove of the fixed cylinder so as to move the movable cam ring in an optical axial direction, shifting the state from collapsing to imaging. At this position in the imaging state, by rotating the movable cam ring without moving it in the optical axial direction, a movable lens is moved in the optical axial direction along the cam groove for moving the lens so as to perform zooming.
Recently, for imaging devices, such as digital cameras, the miniaturization in size and thickness has been demanded, so that in a structure in that a lens barrel is accommodated (collapsed) within an imaging device body, reduction in the entire length of the lens barrel in an accommodated (collapsed) state is required.
In the lens barrel disclosed in Japanese Patent Laid-Open No. 2001-324663 mentioned above, since zooming is performed in an imaging mode, by rotating a movable cam-ring without moving it in the optical axial direction so as to move a movable lens in the optical axial direction along a cam groove for moving a lens, the cam groove for moving a lens is necessary to be formed corresponding to the displacement (zooming amount), so that in accordance with this displacement, the entire length of the movable cam-ring in the optical axial direction is required to be long. Thus, the entire length of the lens barrel is increased in a collapsed state in that the lens barrel is accommodated within the imaging device body. Also, in an optical system in that the movable lens at the wide end is different in position from that at the telescopic end, in the zooming region along the optical axis (the extended displacement of the movable lens at the wide end is different from that at the telescopic end), the length of the cam groove for moving a lens is further increased, so that the entire length of the movable cam-ring in the optical axial direction is further elongated. Also, because of steep changes in cam profile, the torque for rotating the movable cam-ring is increased.